EDEN PRAIRIE, Minn. -- Minnesota Vikings middle linebacker E.J. Henderson sat out practice Thursday because of swelling in one of his knees and underwent a precautionary X-ray.

The X-ray showed no structural damage, an NFL source said late Thursday, and the plan was to reevaluate Henderson on Friday morning.

The issue came to light when Henderson arrived at Vikings headquarters on Thursday morning and "was sore," coach Leslie Frazier said. The team "just thought it would be wise with his knee being sore to hold him back a little bit," Frazier said.

Henderson went through all of Wednesday's practice but had swelling in the knee on Thursday morning. The team did not plan to put him through an MRI, just the X-ray.

"(It's) precautionary," Frazier said. "We'll see how he feels (Friday) when he wakes up. If there's a problem (Friday), then you start getting a little more concerned."

The Vikings will host to Tampa Bay on Sunday in their home opener.

Henderson was replaced at middle linebacker in Thursday's practice by Xavier Adibi and Erin Henderson, who is the starter on the weakside. Adibi was claimed off waivers from Houston this month. When Erin Henderson moved to the middle, Kenny Onatolu played on the weakside.

Abibi played in a 3-4 defense with the Texans, but Frazier said he has become more comfortable playing the middle linebacker in the 4-3. "He played inside backer and some of the terminology (the Texans) use is similar to ours," Frazier said. "He's been with us now for a few weeks so he's more comfortable."

The Vikings coaches plan to look at the practice film from Thursday to see who might start in the middle if E.J. Henderson can't go. Henderson is due to make $4.7 million this season in the final year of his contract.

The veteran was named to the Pro Bowl last season after starting all 16 games and finishing second on the team with 139 tackles. That came after Henderson had his 2009 season ended on Dec. 6 when he suffered a broken femur in his left leg in Arizona.

Defensive end Adrian Awasom sat out a second consecutive practice because of swelling in his knee. "He should be able to practice (Friday)," Frazier said.

Cornerback Asher Allen (toe) and wide receiver Michael Jenkins (groin) remained on the injury report but again did not miss any practice time.